/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hama.ipc;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ConnectException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketTimeoutException;
import java.net.UnknownHostException;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;

import javax.net.SocketFactory;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.DataOutputBuffer;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableUtils;
import org.apache.hadoop.security.SaslRpcServer.AuthMethod;
import org.apache.hadoop.security.UserGroupInformation;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.hama.util.BSPNetUtils;

/**
 * A client for an IPC service. IPC calls take a single {@link Writable} as a
 * parameter, and return a {@link Writable} as their value. A service runs on a
 * port and is defined by a parameter class and a value class.
 * 
 * @see Server
 */
public class Client {
  public static final String IPC_CLIENT_CONNECT_MAX_RETRIES_KEY = "ipc.client.connect.max.retries";
  public static final int IPC_CLIENT_CONNECT_MAX_RETRIES_DEFAULT = 10;

  public static final Log LOG = LogFactory.getLog(Client.class);
  private Hashtable<ConnectionId, Connection> connections = new Hashtable<ConnectionId, Connection>();

  private Class<? extends Writable> valueClass; // class of call values
  private int counter; // counter for call ids
  private AtomicBoolean running = new AtomicBoolean(true); // if client runs
  final private Configuration conf;

  private SocketFactory socketFactory; // how to create sockets
  private int refCount = 1;

  final private static String PING_INTERVAL_NAME = "ipc.ping.interval";
  final static int DEFAULT_PING_INTERVAL = 60000; // 1 min
  final static int PING_CALL_ID = -1;

  /**
   * set the ping interval value in configuration
   * 
   * @param conf Configuration
   * @param pingInterval the ping interval
   */
  final public static void setPingInterval(Configuration conf, int pingInterval) {
    conf.setInt(PING_INTERVAL_NAME, pingInterval);
  }

  /**
   * Get the ping interval from configuration; If not set in the configuration,
   * return the default value.
   * 
   * @param conf Configuration
   * @return the ping interval
   */
  final static int getPingInterval(Configuration conf) {
    return conf.getInt(PING_INTERVAL_NAME, DEFAULT_PING_INTERVAL);
  }

  /**
   * The time after which a RPC will timeout. If ping is not enabled (via
   * ipc.client.ping), then the timeout value is the same as the pingInterval.
   * If ping is enabled, then there is no timeout value.
   * 
   * @param conf Configuration
   * @return the timeout period in milliseconds. -1 if no timeout value is set
   */
  final public static int getTimeout(Configuration conf) {
    if (!conf.getBoolean("ipc.client.ping", true)) {
      return getPingInterval(conf);
    }
    return -1;
  }

  /**
   * Increment this client's reference count
   * 
   */
  synchronized void incCount() {
    refCount++;
  }

  /**
   * Decrement this client's reference count
   * 
   */
  synchronized void decCount() {
    refCount--;
  }

  /**
   * Return if this client has no reference
   * 
   * @return true if this client has no reference; false otherwise
   */
  synchronized boolean isZeroReference() {
    return refCount == 0;
  }

  /** A call waiting for a value. */
  private class Call {
    int id; // call id
    Writable param; // parameter
    Writable value; // value, null if error
    IOException error; // exception, null if value
    boolean done; // true when call is done

    protected Call(Writable param) {
      this.param = param;
      synchronized (Client.this) {
        this.id = counter++;
      }
    }

    /**
     * Indicate when the call is complete and the value or error are available.
     * Notifies by default.
     */
    protected synchronized void callComplete() {
      this.done = true;
      notify(); // notify caller
    }

    /**
     * Set the exception when there is an error. Notify the caller the call is
     * done.
     * 
     * @param error exception thrown by the call; either local or remote
     */
    public synchronized void setException(IOException error) {
      this.error = error;
      callComplete();
    }

    /**
     * Set the return value when there is no error. Notify the caller the call
     * is done.
     * 
     * @param value return value of the call.
     */
    public synchronized void setValue(Writable value) {
      this.value = value;
      callComplete();
    }
  }

  /**
   * Thread that reads responses and notifies callers. Each connection owns a
   * socket connected to a remote address. Calls are multiplexed through this
   * socket: responses may be delivered out of order.
   */
  private class Connection extends Thread {
    private InetSocketAddress server; // server ip:port
    private ConnectionHeader header; // connection header
    private final ConnectionId remoteId; // connection id
    private AuthMethod authMethod; // authentication method

    private Socket socket = null; // connected socket
    private DataInputStream in;
    private DataOutputStream out;
    private int rpcTimeout;
    private int maxIdleTime; // connections will be culled if it was idle for
    // maxIdleTime msecs
    private final RetryPolicy connectionRetryPolicy;
    private boolean tcpNoDelay; // if T then disable Nagle's Algorithm
    private int pingInterval; // how often sends ping to the server in msecs

    // currently active calls
    private Hashtable<Integer, Call> calls = new Hashtable<Integer, Call>();
    private AtomicLong lastActivity = new AtomicLong();// last I/O activity time
    private AtomicBoolean shouldCloseConnection = new AtomicBoolean(); // indicate
                                                                       // if the
                                                                       // connection
                                                                       // is
                                                                       // closed
    private IOException closeException; // close reason

    public Connection(ConnectionId remoteId) throws IOException {
      this.remoteId = remoteId;
      this.server = remoteId.getAddress();
      if (server.isUnresolved()) {
        throw new UnknownHostException("unknown host: "
            + remoteId.getAddress().getHostName());
      }
      this.maxIdleTime = remoteId.getMaxIdleTime();
      this.connectionRetryPolicy = remoteId.connectionRetryPolicy;
      this.tcpNoDelay = remoteId.getTcpNoDelay();
      this.pingInterval = remoteId.getPingInterval();
      if (LOG.isDebugEnabled()) {
        LOG.debug("The ping interval is" + this.pingInterval + "ms.");
      }
      this.rpcTimeout = remoteId.getRpcTimeout();
      UserGroupInformation ticket = remoteId.getTicket();
      Class<?> protocol = remoteId.getProtocol();

      /*
       * NOTE: We don't support security mode.
       */
      authMethod = AuthMethod.SIMPLE;

      header = new ConnectionHeader(protocol == null ? null
          : protocol.getName(), ticket, authMethod);

      if (LOG.isDebugEnabled())
        LOG.debug("Use " + authMethod + " authentication");

      this.setName("IPC Client (" + socketFactory.hashCode()
          + ") connection to " + remoteId.getAddress().toString() + " from "
          + ((ticket == null) ? "an unknown user" : ticket.getUserName()));
      this.setDaemon(true);
    }

    /** Update lastActivity with the current time. */
    private void touch() {
      lastActivity.set(System.currentTimeMillis());
    }

    /**
     * Add a call to this connection's call queue and notify a listener;
     * synchronized. Returns false if called during shutdown.
     * 
     * @param call to add
     * @return true if the call was added.
     */
    private synchronized boolean addCall(Call call) {
      if (shouldCloseConnection.get())
        return false;
      calls.put(call.id, call);
      notify();
      return true;
    }

    /**
     * This class sends a ping to the remote side when timeout on reading. If no
     * failure is detected, it retries until at least a byte is read.
     */
    private class PingInputStream extends FilterInputStream {
      /* constructor */
      protected PingInputStream(InputStream in) {
        super(in);
      }

      /*
       * Process timeout exception if the connection is not going to be closed
       * or is not configured to have a RPC timeout, send a ping. (if rpcTimeout
       * is not set to be 0, then RPC should timeout. otherwise, throw the
       * timeout exception.
       */
      private void handleTimeout(SocketTimeoutException e) throws IOException {
        if (shouldCloseConnection.get() || !running.get() || rpcTimeout > 0) {
          throw e;
        } else {
          sendPing();
        }
      }

      /**
       * Read a byte from the stream. Send a ping if timeout on read. Retries if
       * no failure is detected until a byte is read.
       * 
       * @throws IOException for any IO problem other than socket timeout
       */
      public int read() throws IOException {
        do {
          try {
            return super.read();
          } catch (SocketTimeoutException e) {
            handleTimeout(e);
          }
        } while (true);
      }

      /**
       * Read bytes into a buffer starting from offset <code>off</code> Send a
       * ping if timeout on read. Retries if no failure is detected until a byte
       * is read.
       * 
       * @return the total number of bytes read; -1 if the connection is closed.
       */
      public int read(byte[] buf, int off, int len) throws IOException {
        do {
          try {
            return super.read(buf, off, len);
          } catch (SocketTimeoutException e) {
            handleTimeout(e);
          }
        } while (true);
      }
    }

    /**
     * Update the server address if the address corresponding to the host name
     * has changed.
     * 
     * @return true if an addr change was detected.
     * @throws IOException when the hostname cannot be resolved.
     */
    private synchronized boolean updateAddress() throws IOException {
      // Do a fresh lookup with the old host name.
      InetSocketAddress currentAddr = BSPNetUtils.makeSocketAddr(
          server.getHostName(), server.getPort());

      if (!server.equals(currentAddr)) {
        LOG.warn("Address change detected. Old: " + server.toString()
            + " New: " + currentAddr.toString());
        server = currentAddr;
        return true;
      }
      return false;
    }

    private synchronized void setupConnection() throws IOException {
      short ioFailures = 0;
      short timeoutFailures = 0;
      while (true) {
        try {
          this.socket = socketFactory.createSocket();
          this.socket.setTcpNoDelay(tcpNoDelay);

          // connection time out is 20s
          BSPNetUtils.connect(this.socket, server, 20000);
          if (rpcTimeout > 0) {
            pingInterval = rpcTimeout; // rpcTimeout overwrites pingInterval
          }

          this.socket.setSoTimeout(pingInterval);
          return;
        } catch (SocketTimeoutException toe) {
          /*
           * Check for an address change and update the local reference. Reset
           * the failure counter if the address was changed
           */
          if (updateAddress()) {
            timeoutFailures = ioFailures = 0;
          }
          /*
           * The max number of retries is 45, which amounts to 20s*45 = 15
           * minutes retries.
           */
          handleConnectionFailure(timeoutFailures++, 45, toe);
        } catch (IOException ie) {
          if (updateAddress()) {
            timeoutFailures = ioFailures = 0;
          }
          handleConnectionFailure(ioFailures++, ie);
        }
      }
    }

    /**
     * Connect to the server and set up the I/O streams. It then sends a header
     * to the server and starts the connection thread that waits for responses.
     */
    private synchronized void setupIOstreams() throws InterruptedException {
      if (socket != null || shouldCloseConnection.get()) {
        return;
      }

      try {
        if (LOG.isDebugEnabled()) {
          LOG.debug("Connecting to " + server);
        }

        while (true) {
          setupConnection();
          InputStream inStream = BSPNetUtils.getInputStream(socket);
          OutputStream outStream = BSPNetUtils.getOutputStream(socket);
          writeRpcHeader(outStream);
          this.in = new DataInputStream(new BufferedInputStream(
              new PingInputStream(inStream)));
          this.out = new DataOutputStream(new BufferedOutputStream(outStream));
          writeHeader();

          // update last activity time
          touch();

          // start the receiver thread after the socket connection has been set
          // up
          start();
          return;
        }
      } catch (Throwable t) {
        if (t instanceof IOException) {
          markClosed((IOException) t);
        } else {
          markClosed(new IOException("Couldn't set up IO streams", t));
        }
        close();
      }
    }

    private void closeConnection() {
      // close the current connection
      try {
        socket.close();
      } catch (IOException e) {
        LOG.warn("Not able to close a socket", e);
      }
      // set socket to null so that the next call to setupIOstreams
      // can start the process of connect all over again.
      socket = null;
    }

    /*
     * Handle connection failures If the current number of retries is equal to
     * the max number of retries, stop retrying and throw the exception;
     * Otherwise backoff 1 second and try connecting again. This Method is only
     * called from inside setupIOstreams(), which is synchronized. Hence the
     * sleep is synchronized; the locks will be retained.
     * @param curRetries current number of retries
     * @param maxRetries max number of retries allowed
     * @param ioe failure reason
     * @throws IOException if max number of retries is reached
     */
    private void handleConnectionFailure(int curRetries, int maxRetries,
        IOException ioe) throws IOException {

      closeConnection();

      // throw the exception if the maximum number of retries is reached
      if (curRetries >= maxRetries) {
        throw ioe;
      }

      // otherwise back off and retry
      try {
        Thread.sleep(1000);
      } catch (InterruptedException ignored) {
      }

      LOG.info("Retrying connect to server: " + server + ". Already tried "
          + curRetries + " time(s); maxRetries=" + maxRetries);
    }

    private void handleConnectionFailure(int curRetries, IOException ioe)
        throws IOException {
      closeConnection();

      final boolean retry;
      try {
        retry = connectionRetryPolicy.shouldRetry(ioe, curRetries);
      } catch (Exception e) {
        throw e instanceof IOException ? (IOException) e : new IOException(e);
      }
      if (!retry) {
        throw ioe;
      }

      LOG.info("Retrying connect to server: " + server + ". Already tried "
          + curRetries + " time(s); retry policy is " + connectionRetryPolicy);
    }

    /* Write the RPC header */
    private void writeRpcHeader(OutputStream outStream) throws IOException {
      DataOutputStream out = new DataOutputStream(new BufferedOutputStream(
          outStream));
      // Write out the header, version and authentication method
      out.write(Server.HEADER.array());
      out.write(Server.CURRENT_VERSION);
      authMethod.write(out);
      out.flush();
    }

    /*
     * Write the protocol header for each connection Out is not synchronized
     * because only the first thread does this.
     */
    private void writeHeader() throws IOException {
      // Write out the ConnectionHeader
      DataOutputBuffer buf = new DataOutputBuffer();
      header.write(buf);

      // Write out the payload length
      int bufLen = buf.getLength();
      out.writeInt(bufLen);
      out.write(buf.getData(), 0, bufLen);
    }

    /*
     * wait till someone signals us to start reading RPC response or it is idle
     * too long, it is marked as to be closed, or the client is marked as not
     * running. Return true if it is time to read a response; false otherwise.
     */
    private synchronized boolean waitForWork() {
      if (calls.isEmpty() && !shouldCloseConnection.get() && running.get()) {
        long timeout = maxIdleTime
            - (System.currentTimeMillis() - lastActivity.get());
        if (timeout > 0) {
          try {
            wait(timeout);
          } catch (InterruptedException e) {
          }
        }
      }

      if (!calls.isEmpty() && !shouldCloseConnection.get() && running.get()) {
        return true;
      } else if (shouldCloseConnection.get()) {
        return false;
      } else if (calls.isEmpty()) { // idle connection closed or stopped
        markClosed(null);
        return false;
      } else { // get stopped but there are still pending requests
        markClosed((IOException) new IOException()
            .initCause(new InterruptedException()));
        return false;
      }
    }

    public InetSocketAddress getRemoteAddress() {
      return server;
    }

    /*
     * Send a ping to the server if the time elapsed since last I/O activity is
     * equal to or greater than the ping interval
     */
    private synchronized void sendPing() throws IOException {
      long curTime = System.currentTimeMillis();
      if (curTime - lastActivity.get() >= pingInterval) {
        lastActivity.set(curTime);
        synchronized (out) {
          out.writeInt(PING_CALL_ID);
          out.flush();
        }
      }
    }

    public void run() {
      if (LOG.isDebugEnabled())
        LOG.debug(getName() + ": starting, having connections "
            + connections.size());

      while (waitForWork()) {// wait here for work - read or close connection
        receiveResponse();
      }

      close();

      if (LOG.isDebugEnabled())
        LOG.debug(getName() + ": stopped, remaining connections "
            + connections.size());
    }

    /**
     * Initiates a call by sending the parameter to the remote server. Note:
     * this is not called from the Connection thread, but by other threads.
     */
    public void sendParam(Call call) {
      if (shouldCloseConnection.get()) {
        return;
      }

      DataOutputBuffer d = null;
      try {
        synchronized (this.out) {
          if (LOG.isDebugEnabled())
            LOG.debug(getName() + " sending #" + call.id);

          // for serializing the
          // data to be written
          d = new DataOutputBuffer();
          d.writeInt(call.id);
          call.param.write(d);
          byte[] data = d.getData();
          int dataLength = d.getLength();
          out.writeInt(dataLength); // first put the data length
          out.write(data, 0, dataLength);// write the data
          out.flush();
        }
      } catch (IOException e) {
        markClosed(e);
      } finally {
        // the buffer is just an in-memory buffer, but it is still polite to
        // close early
        IOUtils.closeStream(d);
      }
    }

    /*
     * Receive a response. Because only one receiver, so no synchronization on
     * in.
     */
    private void receiveResponse() {
      if (shouldCloseConnection.get()) {
        return;
      }
      touch();

      try {
        int id = in.readInt(); // try to read an id

        if (LOG.isDebugEnabled())
          LOG.debug(getName() + " got value #" + id);

        Call call = calls.get(id);

        int state = in.readInt(); // read call status
        if (state == Status.SUCCESS.state) {
          Writable value = ReflectionUtils.newInstance(valueClass, conf);
          value.readFields(in); // read value
          call.setValue(value);
          calls.remove(id);
        } else if (state == Status.ERROR.state) {
          call.setException(new RemoteException(WritableUtils.readString(in),
              WritableUtils.readString(in)));
          calls.remove(id);
        } else if (state == Status.FATAL.state) {
          // Close the connection
          markClosed(new RemoteException(WritableUtils.readString(in),
              WritableUtils.readString(in)));
        }
      } catch (IOException e) {
        markClosed(e);
      }
    }

    private synchronized void markClosed(IOException e) {
      if (shouldCloseConnection.compareAndSet(false, true)) {
        closeException = e;
        notifyAll();
      }
    }

    /** Close the connection. */
    private synchronized void close() {
      if (!shouldCloseConnection.get()) {
        LOG.error("The connection is not in the closed state");
        return;
      }

      // release the resources
      // first thing to do;take the connection out of the connection list
      synchronized (connections) {
        if (connections.get(remoteId) == this) {
          connections.remove(remoteId);
        }
      }

      // close the streams and therefore the socket
      IOUtils.closeStream(out);
      IOUtils.closeStream(in);

      // clean up all calls
      if (closeException == null) {
        if (!calls.isEmpty()) {
          LOG.warn("A connection is closed for no cause and calls are not empty");

          // clean up calls anyway
          closeException = new IOException("Unexpected closed connection");
          cleanupCalls();
        }
      } else {
        // log the info
        if (LOG.isDebugEnabled()) {
          LOG.debug("closing ipc connection to " + server + ": "
              + closeException.getMessage(), closeException);
        }

        // cleanup calls
        cleanupCalls();
      }
      if (LOG.isDebugEnabled())
        LOG.debug(getName() + ": closed");
    }

    /* Cleanup all calls and mark them as done */
    private void cleanupCalls() {
      Iterator<Entry<Integer, Call>> itor = calls.entrySet().iterator();
      while (itor.hasNext()) {
        Call c = itor.next().getValue();
        c.setException(closeException); // local exception
        itor.remove();
      }
    }
  }

  /** Call implementation used for parallel calls. */
  private class ParallelCall extends Call {
    private ParallelResults results;
    private int index;

    public ParallelCall(Writable param, ParallelResults results, int index) {
      super(param);
      this.results = results;
      this.index = index;
    }

    /** Deliver result to result collector. */
    protected void callComplete() {
      results.callComplete(this);
    }
  }

  /** Result collector for parallel calls. */
  private static class ParallelResults {
    private Writable[] values;
    private int size;
    private int count;

    public ParallelResults(int size) {
      this.values = new Writable[size];
      this.size = size;
    }

    /** Collect a result. */
    public synchronized void callComplete(ParallelCall call) {
      values[call.index] = call.value; // store the value
      count++; // count it
      if (count == size) // if all values are in
        notify(); // then notify waiting caller
    }
  }

  /**
   * Construct an IPC client whose values are of the given {@link Writable}
   * class.
   */
  public Client(Class<? extends Writable> valueClass, Configuration conf,
      SocketFactory factory) {
    this.valueClass = valueClass;
    this.conf = conf;
    this.socketFactory = factory;
  }

  /**
   * Construct an IPC client with the default SocketFactory
   * 
   * @param valueClass
   * @param conf
   */
  public Client(Class<? extends Writable> valueClass, Configuration conf) {
    this(valueClass, conf, BSPNetUtils.getDefaultSocketFactory(conf));
  }

  /**
   * Return the socket factory of this client
   * 
   * @return this client's socket factory
   */
  SocketFactory getSocketFactory() {
    return socketFactory;
  }

  /**
   * Stop all threads related to this client. No further calls may be made using
   * this client.
   */
  public void stop() {
    if (LOG.isDebugEnabled()) {
      LOG.debug("Stopping client");
    }

    if (!running.compareAndSet(true, false)) {
      return;
    }

    // wake up all connections
    synchronized (connections) {
      for (Connection conn : connections.values()) {
        conn.interrupt();
      }
    }

    // wait until all connections are closed
    while (!connections.isEmpty()) {
      try {
        Thread.sleep(100);
      } catch (InterruptedException e) {
      }
    }
  }

  /**
   * Make a call, passing <code>param</code>, to the IPC server running at
   * <code>address</code>, returning the value. Throws exceptions if there are
   * network problems or if the remote code threw an exception.
   * 
   * @deprecated Use {@link #call(Writable, ConnectionId)} instead
   */
  @Deprecated
  public Writable call(Writable param, InetSocketAddress address)
      throws InterruptedException, IOException {
    return call(param, address, null);
  }

  /**
   * Make a call, passing <code>param</code>, to the IPC server running at
   * <code>address</code> with the <code>ticket</code> credentials, returning
   * the value. Throws exceptions if there are network problems or if the remote
   * code threw an exception.
   * 
   * @deprecated Use {@link #call(Writable, ConnectionId)} instead
   */
  @Deprecated
  public Writable call(Writable param, InetSocketAddress addr,
      UserGroupInformation ticket) throws InterruptedException, IOException {
    ConnectionId remoteId = ConnectionId.getConnectionId(addr, null, ticket, 0,
        conf);
    return call(param, remoteId);
  }

  /**
   * Make a call, passing <code>param</code>, to the IPC server running at
   * <code>address</code> which is servicing the <code>protocol</code> protocol,
   * with the <code>ticket</code> credentials and <code>rpcTimeout</code> as
   * timeout, returning the value. Throws exceptions if there are network
   * problems or if the remote code threw an exception.
   * 
   * @deprecated Use {@link #call(Writable, ConnectionId)} instead
   */
  @Deprecated
  public Writable call(Writable param, InetSocketAddress addr,
      Class<?> protocol, UserGroupInformation ticket, int rpcTimeout)
      throws InterruptedException, IOException {
    ConnectionId remoteId = ConnectionId.getConnectionId(addr, protocol,
        ticket, rpcTimeout, conf);
    return call(param, remoteId);
  }

  /**
   * Make a call, passing <code>param</code>, to the IPC server running at
   * <code>address</code> which is servicing the <code>protocol</code> protocol,
   * with the <code>ticket</code> credentials, <code>rpcTimeout</code> as
   * timeout and <code>conf</code> as configuration for this connection,
   * returning the value. Throws exceptions if there are network problems or if
   * the remote code threw an exception.
   */
  public Writable call(Writable param, InetSocketAddress addr,
      Class<?> protocol, UserGroupInformation ticket, int rpcTimeout,
      Configuration conf) throws InterruptedException, IOException {
    ConnectionId remoteId = ConnectionId.getConnectionId(addr, protocol,
        ticket, rpcTimeout, conf);
    return call(param, remoteId);
  }

  /**
   * Make a call, passing <code>param</code>, to the IPC server defined by
   * <code>remoteId</code>, returning the value. Throws exceptions if there are
   * network problems or if the remote code threw an exception.
   */
  public Writable call(Writable param, ConnectionId remoteId)
      throws InterruptedException, IOException {
    Call call = new Call(param);
    Connection connection = getConnection(remoteId, call);
    connection.sendParam(call); // send the parameter
    boolean interrupted = false;
    synchronized (call) {
      while (!call.done) {
        try {
          call.wait(); // wait for the result
        } catch (InterruptedException ie) {
          // save the fact that we were interrupted
          interrupted = true;
        }
      }

      if (interrupted) {
        // set the interrupt flag now that we are done waiting
        Thread.currentThread().interrupt();
      }

      if (call.error != null) {
        if (call.error instanceof RemoteException) {
          call.error.fillInStackTrace();
          throw call.error;
        } else { // local exception
          // use the connection because it will reflect an ip change, unlike
          // the remoteId
          throw wrapException(connection.getRemoteAddress(), call.error);
        }
      } else {
        return call.value;
      }
    }
  }

  /**
   * Take an IOException and the address we were trying to connect to and return
   * an IOException with the input exception as the cause. The new exception
   * provides the stack trace of the place where the exception is thrown and
   * some extra diagnostics information. If the exception is ConnectException or
   * SocketTimeoutException, return a new one of the same type; Otherwise return
   * an IOException.
   * 
   * @param addr target address
   * @param exception the relevant exception
   * @return an exception to throw
   */
  private IOException wrapException(InetSocketAddress addr,
      IOException exception) {
    if (exception instanceof ConnectException) {
      // connection refused; include the host:port in the error
      return (ConnectException) new ConnectException("Call to " + addr
          + " failed on connection exception: " + exception)
          .initCause(exception);
    } else if (exception instanceof SocketTimeoutException) {
      return (SocketTimeoutException) new SocketTimeoutException("Call to "
          + addr + " failed on socket timeout exception: " + exception)
          .initCause(exception);
    } else {
      return (IOException) new IOException("Call to " + addr
          + " failed on local exception: " + exception).initCause(exception);

    }
  }

  /**
   * @deprecated Use
   *             {@link #call(Writable[], InetSocketAddress[], Class, UserGroupInformation, Configuration)}
   *             instead
   */
  @Deprecated
  public Writable[] call(Writable[] params, InetSocketAddress[] addresses)
      throws IOException, InterruptedException {
    return call(params, addresses, null, null, conf);
  }

  /**
   * @deprecated Use
   *             {@link #call(Writable[], InetSocketAddress[], Class, UserGroupInformation, Configuration)}
   *             instead
   */
  @Deprecated
  public Writable[] call(Writable[] params, InetSocketAddress[] addresses,
      Class<?> protocol, UserGroupInformation ticket) throws IOException,
      InterruptedException {
    return call(params, addresses, protocol, ticket, conf);
  }

  /**
   * Makes a set of calls in parallel. Each parameter is sent to the
   * corresponding address. When all values are available, or have timed out or
   * errored, the collected results are returned in an array. The array contains
   * nulls for calls that timed out or errored.
   */
  public Writable[] call(Writable[] params, InetSocketAddress[] addresses,
      Class<?> protocol, UserGroupInformation ticket, Configuration conf)
      throws IOException, InterruptedException {
    if (addresses.length == 0)
      return new Writable[0];

    ParallelResults results = new ParallelResults(params.length);
    synchronized (results) {
      for (int i = 0; i < params.length; i++) {
        ParallelCall call = new ParallelCall(params[i], results, i);
        try {
          ConnectionId remoteId = ConnectionId.getConnectionId(addresses[i],
              protocol, ticket, 0, conf);
          Connection connection = getConnection(remoteId, call);
          connection.sendParam(call); // send each parameter
        } catch (IOException e) {
          // log errors
          LOG.info("Calling " + addresses[i] + " caught: " + e.getMessage(), e);
          results.size--; // wait for one fewer result
        }
      }
      while (results.count != results.size) {
        try {
          results.wait(); // wait for all results
        } catch (InterruptedException e) {
        }
      }

      return results.values;
    }
  }

  // for unit testing only
  Set<ConnectionId> getConnectionIds() {
    synchronized (connections) {
      return connections.keySet();
    }
  }

  /**
   * Get a connection from the pool, or create a new one and add it to the pool.
   * Connections to a given ConnectionId are reused.
   */
  private Connection getConnection(ConnectionId remoteId, Call call)
      throws IOException, InterruptedException {
    if (!running.get()) {
      // the client is stopped
      throw new IOException("The client is stopped");
    }
    Connection connection;
    /*
     * we could avoid this allocation for each RPC by having a connectionsId
     * object and with set() method. We need to manage the refs for keys in
     * HashMap properly. For now its ok.
     */
    do {
      synchronized (connections) {
        connection = connections.get(remoteId);
        if (connection == null) {
          connection = new Connection(remoteId);
          connections.put(remoteId, connection);
        }
      }
    } while (!connection.addCall(call));

    // we don't invoke the method below inside "synchronized (connections)"
    // block above. The reason for that is if the server happens to be slow,
    // it will take longer to establish a connection and that will slow the
    // entire system down.
    connection.setupIOstreams();
    return connection;
  }

  /**
   * This class holds the address and the user ticket. The client connections to
   * servers are uniquely identified by <remoteAddress, protocol, ticket>
   */
  static class ConnectionId {
    InetSocketAddress address;
    UserGroupInformation ticket;
    Class<?> protocol;
    private static final int PRIME = 16777619;
    private int rpcTimeout;
    private String serverPrincipal;
    private int maxIdleTime; // connections will be culled if it was idle for
    // maxIdleTime msecs
    private final RetryPolicy connectionRetryPolicy;
    private boolean tcpNoDelay; // if T then disable Nagle's Algorithm
    private int pingInterval; // how often sends ping to the server in msecs

    ConnectionId(InetSocketAddress address, Class<?> protocol,
        UserGroupInformation ticket, int rpcTimeout, String serverPrincipal,
        int maxIdleTime, RetryPolicy connectionRetryPolicy, boolean tcpNoDelay,
        int pingInterval) {
      this.protocol = protocol;
      this.address = address;
      this.ticket = ticket;
      this.rpcTimeout = rpcTimeout;
      this.serverPrincipal = serverPrincipal;
      this.maxIdleTime = maxIdleTime;
      this.connectionRetryPolicy = connectionRetryPolicy;
      this.tcpNoDelay = tcpNoDelay;
      this.pingInterval = pingInterval;
    }

    InetSocketAddress getAddress() {
      return address;
    }

    Class<?> getProtocol() {
      return protocol;
    }

    UserGroupInformation getTicket() {
      return ticket;
    }

    private int getRpcTimeout() {
      return rpcTimeout;
    }

    String getServerPrincipal() {
      return serverPrincipal;
    }

    int getMaxIdleTime() {
      return maxIdleTime;
    }

    boolean getTcpNoDelay() {
      return tcpNoDelay;
    }

    int getPingInterval() {
      return pingInterval;
    }

    static ConnectionId getConnectionId(InetSocketAddress addr,
        Class<?> protocol, UserGroupInformation ticket, Configuration conf)
        throws IOException {
      return getConnectionId(addr, protocol, ticket, 0, conf);
    }

    static ConnectionId getConnectionId(InetSocketAddress addr,
        Class<?> protocol, UserGroupInformation ticket, int rpcTimeout,
        Configuration conf) throws IOException {
      return getConnectionId(addr, protocol, ticket, rpcTimeout, null, conf);
    }

    static ConnectionId getConnectionId(InetSocketAddress addr,
        Class<?> protocol, UserGroupInformation ticket, int rpcTimeout,
        RetryPolicy connectionRetryPolicy, Configuration conf)
        throws IOException {

      if (connectionRetryPolicy == null) {
        final int max = conf.getInt(IPC_CLIENT_CONNECT_MAX_RETRIES_KEY,
            IPC_CLIENT_CONNECT_MAX_RETRIES_DEFAULT);
        connectionRetryPolicy = RetryPolicies
            .retryUpToMaximumCountWithFixedSleep(max, 1, TimeUnit.SECONDS);
      }

      String remotePrincipal = getRemotePrincipal(conf, addr, protocol);
      return new ConnectionId(addr, protocol, ticket,
          rpcTimeout,
          remotePrincipal,
          conf.getInt("ipc.client.connection.maxidletime", 10000), // 10s
          connectionRetryPolicy,
          conf.getBoolean("ipc.client.tcpnodelay", false),
          Client.getPingInterval(conf));
    }

    private static String getRemotePrincipal(Configuration conf,
        InetSocketAddress address, Class<?> protocol) throws IOException {
      if (!UserGroupInformation.isSecurityEnabled() || protocol == null) {
        return null;
      }
      return null;
    }

    static boolean isEqual(Object a, Object b) {
      return a == null ? b == null : a.equals(b);
    }

    @Override
    public boolean equals(Object obj) {
      if (obj == this) {
        return true;
      }
      if (obj instanceof ConnectionId) {
        ConnectionId that = (ConnectionId) obj;
        return isEqual(this.address, that.address)
            && this.maxIdleTime == that.maxIdleTime
            && isEqual(this.connectionRetryPolicy, that.connectionRetryPolicy)
            && this.pingInterval == that.pingInterval
            && isEqual(this.protocol, that.protocol)
            && this.rpcTimeout == that.rpcTimeout
            && isEqual(this.serverPrincipal, that.serverPrincipal)
            && this.tcpNoDelay == that.tcpNoDelay
            && isEqual(this.ticket, that.ticket);
      }
      return false;
    }

    @Override
    public int hashCode() {
      int result = connectionRetryPolicy.hashCode();
      result = PRIME * result + ((address == null) ? 0 : address.hashCode());
      result = PRIME * result + maxIdleTime;
      result = PRIME * result + pingInterval;
      result = PRIME * result + ((protocol == null) ? 0 : protocol.hashCode());
      result = PRIME * rpcTimeout;
      result = PRIME * result
          + ((serverPrincipal == null) ? 0 : serverPrincipal.hashCode());
      result = PRIME * result + (tcpNoDelay ? 1231 : 1237);
      result = PRIME * result + ((ticket == null) ? 0 : ticket.hashCode());
      return result;
    }
  }
}
